Radiant energy receiving device



Juy 7 11942. a. wmf? RADIANT ENERGY R @riginal Filed Sem. 1937 5 Sheets-Sheet 2 BEFLECT//VG July 7, 1942. l. WOLFF 2,288,766

RADIANT ENERGY RECEIVING DEVICE Original Filed Sept. 24, 1937 3 SheetS-Sheet 3 Patented July 7, 1942 2,288,766 RADIANT ENERGY RECEIVING DEVICE Irving Wold', Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application September 24, 1937, Serial No. 165,456. Divided and this application July 27, 1940, Serial No. 347,859

(Cl. Z50-150) Claims.

This application is a divisionof my copending application Serial No. 165,456, led September 24, 1937, issued March 1l, 1941, as Patent 2,234,328 for a Radiant energy receiving device.

My invention relates to a device for receiving radiant energy. More specically to a device for making a visible image of an invisible body radiating heatcwaves.

Instruments are now available using photoelectric principles for observing an invisible body radiating waves of a length slightly longerthan light waves. Such instruments will not operate where fog is interposed between the radiating body and the instrument, because the photoelectric means is not responsive to Wave lengths which will penetrate fog.

It is also well known that there are various means for detecting radiant heat' energy of a wave length which will penetrate fog. While such devices can be used to detect and make known the existence of a radiating body, the amount of information conveyed is limited to such detection, and, in some instances, the measurement oi the temperature of the radiating body. I propose to provide means for detecting not only the existence of an invisible body radiating heat but also to produce a visible image of the original heat-radiating body. There are numerous practical applications of my device. For

example, my invention may be used to detect the presence of an aircraft which is invisible to the eye because of fog, by observing the radiation from the engine of said craft; also the movement of the craft may be detected. In a similar manner, the radiation from the smokestacks of vessels and the like may be detected, as well as the direction in which they are moving. A cold body, like an iceberg, will cast a shadow which may be detected.

Another practical use is as an instrumentlanding system for aircraft. If the aircraft landing field is marked with suitable heat radiators, the receiving device located on an aircraft approaching the field may be used to indicate the field or by a suitable arrangement, the angular position of the aircraft with respect to such field, ,even though the eld should be invisible because of weather conditions.

One of the objects of my invention is to provide means for detecting radiant energy.

Another object of my invention is to provide means for producing a visible image corresponding to a body radiating heat.

Another object of my invention is to provide means for detecting the movements of an invisible moving body which is radiating heat waves.

A still further object is to provide means for guiding aircraft by visible indications from desired points which -are produced by devices radiating heat.

An understanding of my inventionv may be best had by reference to the accompanying drawings in which Figures la, 1b, 1c and 1d are schematic drawings to illustrate the theory of the operation of my invention; Figure 2 is a schematic illustration of one embodiment of my invention: Figure 3 is a sectional drawing indicating a heatresponsive element; Figures 4a and 4b represent respectively plan and sectional views ofl an assembly of heat-responsive elements; Figure 5 is a schematic circuit diagram of one arrangement of my invention; and Figure 6 represents a modiiication.

Referring to Fig. 1a, within an evacuated chamber I are positioned the plates 3 and 5 of a capacitor. The rst plate 3 is preferably a flexible metallic diaphragm. The other plate 5 has a surface l which has caesium, whereby it will emit secondary electrons when primary electrons are impinged upon it from an electron gun 9.

If a stream of electrons emitted from the gun 9 are projected along the path II substantially no electrons will strike the secondary emissive surface l. The stream of electrons II will, however. liberate a certain number of electrons (from adjacent emissive surfaces not shown), which Will charge the plate 5 `negatively as indicated. Through suitable circuits (not shown) the other plate 3 will become positively charged. Under normal circumstances, the emissive plate 5 will be negatively charged to approximately 11/2 volts with respect to the nonemissive plate 3.

If the electron stream Il is projected directly at the emissive surface'l, as-shown in Fig. 1b, the primary electrons numbers of secondary electrons. The secondary electrons taken away from 1 will leave the surface positively charged with respect to the plate 3. It has been determined that, after bombardment. the plate with the emissive surface 1 is approximately 3 volts positive with respect to the nonemissive plate 3. The secondary electrons thus liberated charge other plates negatively as mentioned above.

I propose to make use of this phenomenon for heat detection by changing the capacity between the plates when radiant 4energy within the heat spectrum is impressed on the heat receiving debeen suitably treated withl will liberate increasing the emissive surface vice, In Figure 1c I have represented the plates 3 and 5 as being more closely spaced due to the reception of radiation from the heat radiating source |3. While the plates are more closely spaced, the potential of the emissive surface will still be 11/2 volts negative with respect to the non. emissive plate 3 as long as the electron beam is not projected on the emissive surface. However, because the plates are closer together and, therefore, the capacity between them is in creased, there will be a larger number of elecn tronson each of the surfaces. The presence of this larger number of electrons may be detected, as will hereinafter be described.

In Fig. 1d, I have represented the condition corresponding to Fig. 1cl with the additional efiect caused by the impinging of the electronV stream il on the emissive surface As was the case in Fig. 1b, the plate, including the emissive surface, becomes 3 volts positive with respect to the nonemissive plate. However, the radiation from the heat radiating source i3 will bring the plates closer together, thereby increasing their capacity and increasing the number of electrons on the surface of the plates. In the foregoing illustrations, which are offered only as an aid in understanding the theory of operation, it should be understood that theminus and plus (-i-i marks are not intended to represent any actual number of electrons but are merely illustrative of the action of the device under the several conditions described.

Before describing the details of the heat detecting elements, I shall briefly describe the operation of the system by reference to Fig. 2. The dotted arrow l5 represents an invisible body r.- diating heat. The radiations from the body I5 strike a reflector I1 and form a heat image which is represented by the dotted arrow I9. This heat image falls on the cathode ray tube 2| which includes a plurality of heat-responsive elements whose capacity varies as a function of the received radiant energy. These severalcapacities are successively scanned by means of a cathode ray which is deected by impulses derived from the deiiecting source 23.'

The potentials derived from the changes of the capacity of the several heat detecting elements are applied to an amplifier from which the amplied potential changes are impressed on the cathode ray tube 21. The cathode ray of tube 21 is synchronously deected with the deflections in the receiving tube 2|. The impressed potentials control the cathode ray intensity in accordance with the received signals, whereby a visible image 29 appears on the iiuorescent screen and corresponds to the original body I5.

In Fig. 3, I have shown one embodiment of a heat detector in which an insulated form 3| is arranged with a flexible diaphragm 33 on one end and a heat transmitting diaphragm 3 5 on its opposite end. The exible diaphragml 3l is preferably made of duralumin of about .001 of an inch in thickness. The diaphragm 1s stretched sumciently to free it of wrinkles. and it is secured by cementing or clamping so` that a gastight joint is formed between the diaphragm and the member 3|. The second diaphragm may be made oi' any material which freely transmits radiant energy within the heat spectrum: i. e. wave lengths within the far end of the infra-red region or of the order of 5 microns and upwards. Among such materials are rock salt, fluorite and sylvite. 'I'he second diaphragm 35 is also secured surface highly secondary emissive.

to the member 3| by cementing, clamping or the like, to form a gas-tight joint.

The member 3l includes an opening adjacent the second diaphragm 35. This opening is lled with a finely divided carbonaceous material 38, or nely divided or spongy rhodium, platinum, palladium, or the like, which freely gives oi gases when radiant heat is impressed upon them. It has beenfound that such material 'includes a large area for the occlusion of gases. The region adjacent the duralumin diaphragm 33 includes a gas chamber 31. The diaphragm is connected by means of wire 39 which is brought out through the diaphragm 35 or through any other suitable opening which may be hermetically sealed. The iiexible diaphragm 33 corresponds to the diaphragm 3 of Fig. 1a, etc., and moves under the influence of pressure within the gas chamber.

The assembly described above is placed within a metal shell 40. The lower portion of the shell is provided with a gasket 4|. The gasket insulates the assembly from the shell and spaces the flexible diaphragm 33 from the end of the shell whereby a capacitor is formed. It is preferable to make the capacity between the iiexible diaphragm and the endiof the shell large and the capacity between the shell and fixed portions of the assembly small, to thereby permit maximum changes in capacity with varying gas pressures `within the gas chamber 31. The outer surface i2 of the lower end of the shell is treated with silver, caesium, Aor its equivalent, to render the The upper portion of the shell is secured to a second heat transferring diaphragm 38 by cementing,

clamping or the like. The `iunction between the shell and the diaphragm 38 is preferably vacuum tight, so that the gas chamber 31 may be operated over a wide range of gas pressures when the heat-responsive unit is placed within an evacuated envelope, as will be hereinafter described.

The heat-responsive elements of Fig. 3 may be made in any suitable form; for convenience in manufacture I prefer to use cylindrical elements. These elements are arranged in a form t3 which supports and separately insulates the several members which are designated by the reference number 45. It should be understood that the greater the number of elements -fused, the greater will be the detail of the visible image which corresponds to the invisible body radiating heat. The elements 4B may be arranged in an array in the form of a square, rectangle, circle, or any convenient shape.

In Fig. 5 the several heat-detecting elements are shown assembled in the frame 43 and positioned adjacent the end of a cathode ray tube 41 so that the heat-transmitting diaphragms 33--38 are adjacent the end of the cathode ray tube. The end of the tube, instead of being made of glass, which is the customary construction, is

made of rockl salt, iiuorite,.'sylvite or other suitl -able heat-transferring material.

the cathode ray so that it successively scans each of the heat-detecting elements 45 at a frequencyv preferably above the persistence of vision. The scanning of the elements changes the potential of the emissive surface from l1/2 to +3 volts with respect to the potential of the several duralumin diaphragms 33. This change of potential, together with the change in capacity of the several elements by the radiant energy falling on the heat-transparent diaphragms 35, causes changes in current to flow through the resistor 6|. These changes in current are approximately proportional to the changes in capacity, which capacity changes are determined by the radiant heat falling on the several heat-detecting elements 45.

The changes in current establish voltages which are impressed on the input ofV an amplifier 61 whose output circuit is connected to the control grid 69 of a conventional cathode ray tube 1|. The cathode ray tube 1| includes deflecting electrodes 13 which are energized from the scanning source 65.. Because the scanning source is common to the cathode ray tube 41, which includes the heat-detecting element 45, and to the visible image forming tube 1|, 'it will be seen that the tubes are synchronously scanned and the radiant energy falling on the first cathode ray tube will produce impulses which in turn produce images on the uorescent screen of the conventional cathode ray tube 1|. These images will correspond to the original invisible object. It should be understood that the received visible image may be made equal to, larger or smaller than, the received invisible image, which may be made larger or smaller than the invisible body from which the radiation emanated.

The foregoing system requires two cathode ray tubes and a synchronous scanning means. It has the advantage that the receiving cathode ray tube 41 may be remotely positioned with respect to the visible image tube 1|. However, in some installations a less complicated system may be desired.v I have shown such system in Fig. 6. In this gure is shown an evacuated envelope 1li which includes a pair of focusing anodes 15, 11, a fluorescent screen 19, an electron gun assembly 8| and suitably arranged heatdetecting elements 83. The electron gun includes the usual control grid 85, rst anode 81, second anode 89 and deflecting electrodes 9|. The various electrodes are suitably connected to a power source 94 and a scanning source 96.

The cathode ray from the electron gun assembly should be focused on the heat-detecting elements 83. These heat-detecting elements correspond to the element shown in Fig. 3, but are preferably arranged to form a curved surface as shown. In the arrangement of Fig. 5, the emissive surfaces of the heat-responsive elements are charged nega-tively by the secondary electrons which are emitted from other elements. In the present modification substantially all of the secondary electrons from the emissive surfaces are drawn away and refocused to form the visible image on 4the fluorescent screen. Therefore, other means are supplied to charge the emissive surfaces, as, for example, a biasing battery connected as follows: The several duralumin `dia- Awhich is joined to the positive terminal of a biasing battery 86. The negative terminal of the biasing battery is connected to separate resistors 88, which are in turn connected to the shells 92, which are constructed of metal. The separate metal shells are insulated from each other and the; diaphragme so that the several capacities may be separately initially charged by the battery 86.

In the present construction, the plates 93, corresponding to the plates 5 of Fig. la, are made of metal which is suitably treated by caesium or the like to make the surfaces electron emissive. While a parabolic reflector may be used to focus the image on the heat-transparent end of the tube 13, I have shown, for the purpose of illustrating a modification of my invention which may be applied to the system of Fig. 2, a heat lens 95. The heat lens is made of Bakelite, fiuorite or the like and positioned in front of the tube 13 so that the image 91 of the invisible heat-radiating body is focused on the heat-detecting elements 83, although for convenience of illustration the image is shown in front of the elements 83.

The operation of the present device differs somewhat from the embodiment illustrated by Fig. 5. In Fig. 6 the electrons liberated from the emissive surfaces lof the several elements 83 by thecathode ray from the electron gun 8| are impinged on the screen 19 and focused thereon by the several anodes 15-11. The iiuorescent screen 19 will directly indicate a visible image corresponding to the invisible heat image 91. The foregoing embodiment avoids the necessity of synchronous scanning and separate tubes.

Thus I have described a heat-responsive detector which may be arranged to generate a visible image which corresponds to the image of the invisible body or object whose heat radiations are being detected. It will be apparent that not only will the image be detected but the device will also indicate movements of an invisible body. While I have described the device as a heat wave receiver, it should be understood that, if the remote invisible body is at a substantially lower temperature than the heat receiver device, it will nevertheless be detected and a visible image or shadow may be formed.

I claim as my invention:

1. A heat-detecting device including in combination, an evacuated envelope including a heattransparent portion, and within said envelope a heat-detecting element including a chamber, a material confined within said chamber, said material being capable of releasing gas upon application of heat, a flexible diaphragm, means for applying said gas to said flexible diaphragm whereby the diaphragmis actuated as a function of said gas pressure, a plate spacedfrom said diaphragm and forming a capacity therewith, an electron-emissive surface attached to said plate, and means for directing an electron beam against said emissive surface whereby secondary electrons are emitted as a function of said capacity.

2. A heat-detecting devicel including in comated as a function of said gas pressure, a plateA spaced from said diaphragm .and forming a caments, ysaid elements each including a `capacitor.

whose capacity varies las a function of the applied Aincluding` f said. capacitors to a predetermined potential, means for scanning said emissive ksurface with an electron beam whereby secondary electrons are emitted in numbers which vary as a function of said capacity, a fluorescent screen, and means for focusing said secondaryelectrons on said screen whereby a visible image corresponding to said inf yvisible body is formed.

5. A Aheat-fdetecting device including in ccmbination, an evacuated envelope including a heat-'- transparent portion, and within said envelope a f heat-detecting element including a chamber, a

radiant energy, said capacitors each including a secondary' emissive surface, means for charging said capacitors, means for'scannine said emissive surfaces with an electron beam whereby second-l ary electrons areemitted in numbers which vary 'as a function of said capacity, 'a duorescenty screen, and means for focusing said secondary electrons on'said screen whereby a visible image corresponding to said invisible body is formed.

4. A radiant energy-receiving device including in combination an array of heat responsive elements, said elements each includingr a capacitory Whose capacity varies as a function o the applied yradiant energy, said capacitors each including ya secondary @missive surfacapmeans for charging material conned within said chamber, said material rbeing capable of releasing lgas upon application of heat, a iiexible diaphragm, means for Aapplying said gas to said flexible diaphragm whereby the diaphragm Ais actuated las afunction ci said g'as pressure. a plate spaced from said l diaphragm and forming a capacity therewith, an

.electron emissive surface attachedA to said plate, means for .directing an lelectron beam .against said emissive surface wherebyr secondaryelectrons are emitted as a function oi'said capacity, rvand, meam independent of said electron beam for charging saidr capacity to a predetermined potential.

y IRVlNG WOLE'F. 

